package/berkeleydb: fix shared-only build

Changeset f1d3e098 (Build shared libraries only as the default) broke the
berkeleydb package.

For some reason, we had a very strange post-configure action in bdb:
        $(SED) 's/\.lo/.o/g' $(@D)/build_unix/Makefile

This means that it is using non-libtool object files. This breaks
building shared-only.

This code has been present almost the whole time we've had a berkeleydb
package, that is:
  - November 2003: use a sed expression instead of perl
  - March 2003   : use a perl program
  - August 2002  : introduce berkeleydb

Getting rid of this sed expression fixes the build, and allows building
the three new static/shared combinations: static only, shared only,
both static and shared.

Fixes numerous build failures:
    http://autobuild.buildroot.net/results/b41/b41e13ec6c13830667770b3731f8990062f202bd/
    http://autobuild.buildroot.net/results/925/925433ef505b190aa5ac83c23e9359afe4b21829/
    http://autobuild.buildroot.net/results/9af/9afa0dd835af079411a2ea5d94e5e4db7c993111/


    ...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <jacmet@uclibc.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>